This invention relates to double containment pipes and fittings and to methods for making the same.
Double containment pipelines are in common use for transporting contaminants and toxins underground. They are most commonly used as underground gasoline transporting pipelines.
A double containment pipe or pipeline section is in essence a pipe within a pipe. An inner or primary pipe is the primary carrier of the fluids while the outer or secondary pipe is used to contain any leakage from the primary pipe. An annulus is formed between the pipes. Typically, double containment pipes are formed by slipping a secondary pipe over the primary pipe. The secondary pipe is typically the next largest size after the primary pipe.
Slipping one pipe over the other is a cumbersome, time consuming process in that the primary pipe is formed separately from the secondary pipe and then put together. Moreover, this approach is not conducive to forming double containment pipe sections having curvatures such as double containment fittings. Sometimes the primary pipe is impact damaged before or during the process of being slipped into the secondary pipe. If the primary pipe is made from a composite material, such damage may not be capable of being detected by the human eye. As a result, double containment pipes formed using this method may be undetectably damaged from the onset.
To detect leakage of the primary pipe a sump is generally placed at the lowest point of the pipeline. The sump is typically connected to a lower portion of the annulus formed between the primary and secondary pipe. Any fluid leaked from the primary pipe will travel in the annulus and will collect in the sump. The sump is periodically monitored to determine if there has been leakage. A sensor may be placed in the sump for detecting the accumulation of fluids. A disadvantage with this leak monitoring approach is that it is not instantaneous, i.e., a leak from the primary pipe that is located far enough upstream from the sump would not be detected until the leaked fluid has traveled down the pipeline and into the sump.
During installation and initial inspection of double containment pipes, leakage may be detected by visual inspection of the primary pipe. To accomplish this type of inspection, the secondary pipe is telescoped away from the primary pipe. This is also a time consuming, costly process.
Accordingly, there is needed a method for efficiently manufacturing double containment pipe sections, and a system for rapidly detecting leaks from the primary pipe in a double containment pipe section during initial installation and service.